The present invention generally relates to terminals for telecommunications and more particularly to a mixed mode telecommunication terminal having a capability of communicating in the Class-III of the G4 facsimile system.
In the ISDN (Integrated Service Digital Network) system, various terminal apparatuses are used. One example is the G4 facsimile terminals used as a facsimile apparatus for image transmission, a teletex terminal for character transmission, and a mixed mode terminal for documents. In the last mode, character information and image information are mixed in a single document.
Conventionally, the function of the mixed mode terminal is realized in the Class-III terminal of the G4 facsimile system. In such a mixed mode terminal, a mixed mode document is formed for transmission from character data inputted through a keyboard and image data inputted by scanning an image. When transmitting the mixed mode document, the character data and the image data are transmitted separately. In the reception side terminal, the original mixed mode document is recovered from the transmitted character data and the image data and subsequently outputted for display or printing on a sheet.
In such a conventional mixed mode terminal, the type face such as the font and size of the characters than can be transmitted is usually limited, according to the CCITT recommendation, to those shown in TABLE I.
TABLE I ______________________________________ type face character size ______________________________________ ordinary 1/2 1/1 2/1 bold 1/2 1/1 2/1 italic 1/2 1/1 2/1 ______________________________________
Because of the restriction in the font and size of the characters that are allowed for transmission in the mixed mode, the conventional Class-III terminal of the G4 facsimile has been unable to transmit versatile documents such as those created by the DTP (desk-to-publishing) system. In addition, there has been an inconvenience such that documents including line images like tables and block diagrams, have to be converted to the image data before the transmission. When the G4 facsimile terminal has not the function of converting the line data to the image data, then one cannot achieve the transmission of the line data at all.
In such circumstances, there has been no alternative but to output the entire document once on a recording sheet and transmit the document after conversion into bit map data. Thereby, the bit map data is transmitted as the Class-I data (image data) of the G4 facsimile system. When this procedure is followed, however, there occurs an increase in the information to be transmitted and the efficiency in the transmission is inevitably deteriorated.
Further, it should be noted that, in the foregoing case, the advantage achieved by the Class-III of the G4 facsimile system may be lost almost. More specifically, in the Class-III transmission, the character data is transmitted in the form of character codes, and because of this, an excellent quality in the reproduced character image is guaranteed as long as a high resolution plotter is employed in the reception side terminal. This holds true even when the resolution of image scanning in the transmission side terminal is poor. Obviously, this advantage is not enjoyed when the character data is transmitted after conversion into the image data by scanning in the transmission side terminal. About the increase in the information to be transmitted, it should be noted that the amount of information needed for transmitting the character codes is much smaller than the case of transmitting the image data.